Common allosteric mechanisms between ryanodine and inositol-1,4,5-trisphosphate receptors

Ryanodine receptors (RyRs) are calcium release channels found in the membrane of the endoplasmic reticulum (ER). We recently described the crystal structure of the RyR1 N-terminal disease hot spot. It is built up by three domains that show clear structural homology with the inositol-1,4,5-triphosphate (IP3) binding core and suppressor domain of IP3 receptors (IP3Rs) . Here we analyze the structural features of the domains in both calcium release channels, and propose a model for the closed state of the IP3R N-terminal region. This model explains the effect of the suppressor domain on the affinity for IP3 and is supported by mutational studies performed previously. We propose a mechanism whereby opening of both RyR and IP3R is allosterically coupled to a displacement of the N-terminal domain from the following two domains. This displacement can be affected by disease mutations, glutathionylation of a highly reactive cysteine residue, or ligand binding.